Bill Kirchhofer, of Mt. Washington, Kentucky, has done something most of us dream about but never have the resources or know-how to do-engineer a totally new induction system for a ZR-1 fire-spewing Corvette. Since he's the professional, we decided to let him tell the story.
"The car was purchased in 1998 from a 757 pilot who questioned what was I going to do with the car. I replied that it was to become a project car, explaining about the future plans I had in mind. I don't think he ever believed me, though.
"It was in above-average condition with a completely unmolested stock drivetrain. My goal was to build the ultimate ZR-1, reengineering the engine, suspension, and drivetrain. By 2002, the plans were made and started, as a totally new induction system was being designed to place on top of a streetable 415ci block. The hope was to reach near 650 horses on pump gas using stock intake ports with a bolt-on 'top end.'
"The first step was to dimension every aspect of the engine from the cylinder heads up, which included all of the stock parts to establish a relationship to the new system (bolt holes, ports, water-passage locations, and so on). This was accomplished by using an original Lotus one-to-one-scaled drawing, many stock parts, and many hours of auto CAD modeling by the chief mechanical engineer, my son, Dillon Kirchhofer. A working prototype had to handle all of the physical constraints of the hood, air-conditioning compressor, throttle body, crankcase ventilation, ignition module, and so on. The induction system also had to be able to flow enough air for the engine that now was 65 cubic inches larger.
"There were also the other desired aspects that would be included into the new top end. First, the port runners were straightened and sized to produce the maximum air velocity (torque), while providing sufficient air quantity (hp). The fuel injectors were relocated to increase fuel atomization as we eliminated the fuel-injector boss inside the intake port that provided cleaner airflow and increased air speed, as well as a larger holding area for crankcase ventilation that improved the separation of oil in the air.
"Second on the list was the design functionality. The OEM design places the fuel injectors and fuel rails under the plenum. The new injector housings have the fuel-delivery system on the outside of the plenum and injector housings. This provides several benefits. The first is the ease of removing the wiring harness from an injector to test for the proper ohm reading of an injector. This allows the ability to simply remove the plenum top, flip the ignition key, look inside the ports, and check for a leaking injector. The last major item on the list was a design requirement, pure cosmetic appeal. Frankly, it had to look awesome.
"The final working prototype carried the same qualities and appeal as that of the sheetmetal induction system found on many high-performance drag cars. The development of the casting was made possible through working with the professors of mechanical engineering at the University of Louisville and their state-of-the-art CAD and laser equipment. The process of making the wax model consisted of building each injector housing in two pieces and bonding them together. The individual parts were built in .003-inch layers, and the time required to run the set was a little over 17 hours.
"The peak numbers after one session on the chassis dyno were 543 rear-wheel horsepower and 458 lb-ft torque at 7,500 rpm. Peak horsepower was reached at 7,400 rpm and max torque was at 5,800 rpm. The torque band held a solid 440-plus rear-wheel torque between 4,200 and 6,300 rpm. Using a computation of 18 percent (loss of power due to parasitic drivetrain drag), the numbers translate into over 640 hp and 540 lb-ft at the shaft. The engine is now coupled to a 14.5-inch, lightweight-aluminum billet flywheel, a carbon-ceramic clutch disc, and a 2,500-pound pressure plate to hold the increased torque. The final phase will be to completely port the intake runners on the heads and injector housings, polish and port-match the new injector housings and heads, which will increase the airflow to a point where the engine will be capable of producing a streetable 700 hp at the shaft or 600 hp at the rear wheels, and all on pump gas on 93 octane!"
Bill Kirchhofer ended up with a one-out-of-one, rip-snorting ZR-1 that looks like a sleeper. Even with the heritage the famed ZR-1 carried, pulling up on Bill might prove to be a little humbling. It just goes to show that determination behind a great-though somewhat wild-idea can provide outstanding circumstances. But we're wondering if Bill will let loose his secrets to his fellow Corvette enthusiasts.